1. Field of the Invention
The present invention relates to a direct methanol fuel cell system, a portable electronic appliance having this direct methanol fuel cell system, and a method of detecting an amount of liquid fuel remaining in the direct methanol type fuel cell system.
2. Description of the Related Art
Recently, there is an increasing expectation toward the fuel cell as the power supply of portable electronic appliances supporting the electronic society, or as the power supply for preventing air pollution or global warming.
Among fuel cells, the direct methanol fuel cell (DMFC) for generating power by taking out protons directly from methanol is highly expected to be used in various applications, including the use in portable electronic appliances because a reformer is not needed and the required fuel volume is small.
As disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2001-93551, the liquid fuel container of the direct methanol fuel cell is realized as a detachable container or a liquid fuel refilling container, and therefore the fuel cell is reduced in size and the driving time is extended.
When the direct methanol fuel cell disclosed in this publication is used as the power supply for a portable electronic appliance such as a portable personal computer, as the remaining level decreases in the liquid fuel container, it requires a mechanism for transferring the operation of the electronic appliance to a wait operation, and turning off the power without damaging a hard disk such as a memory incorporated in the portable electronic appliance. The remaining level required for the wait operation is usually about several cubic centimeters although varies depending on the type of the electronic appliance.
For detection of the remaining level, for example, a liquid level sensor using an optical technique is used. However, since the measuring precision is low for the amount of several cubic centimeters, normal operation may be continued without transferring to a wait operation in spite of the shortage of remaining level, and the power generation of the fuel cell may be stopped due to consumption of liquid fuel, so that the electronic appliance may be damaged.